Four experimental cancer treatments that may one day help gravely ill children are facing review by U.S. pediatric advisers who have been working for years to find ways to develop more drugs for this underserved population. The medicines from GlaxoSmithKline Plc (GSK), Amgen (AMGN) Inc., Threshold Pharmaceuticals Inc. (THLD) and Boehringer Ingelheim GmbH have the potential to treat children with a variety of tumors and fast-spreading leukemia. The pediatric advisers to the Food and Drug Administration, in a meeting today, will discuss how best to test the medicines in sophisticated clinical trials in kids that may eventually lead to marketing approval. Companies typically gain clearance for cancer medicines in adults first and then take the time to learn more about the drugs’ potential in younger patients, a smaller and less profitable market. That approach, though, has led to only 15 such medicines being allowed for use in children since 1998. Childhood cancers are “therapeutic orphans,” said Richard O’Reilly, chairman of the Department of Pediatrics at the Memorial Sloan-Kettering Cancer Center in New York. “We have long wanted to have access to promising drugs earlier in their development for kids.” About 10,000 children develop cancer over the course of a year, O’Reilly said, or less than 1 percent of the 1.6 million people in the U.S. who the American Cancer Society estimates will develop the disease this year.